Thermal capillary waves in colloid–polymer mixtures in water

We develop two colloid–polymer mixtures in water and study their phase and interface behaviour by means of confocal scanning laser microscopy. The systems consist either of silica or of poly(methylmethacrylate) particles, fluorescently labelled, with, as the polymer, xanthan. The fluid–fluid phase separation can be clearly followed in time and, depending on the concentrations and system details, we observe coarsening either of a bicontinuous spinodal structure or of a suspension of colloid-rich droplets. After phase separation has completed, we study the thermal capillary waves at the fluid–fluid interface. We construct correlation functions and compare with capillary wave theory. Finally, we demonstrate that these colloid–polymer systems are compatible with microfluidics.